JPH0552991A - Reactor feed water controller - Google Patents

Abstract

PURPOSE:To obtain a reactor feed water controller having a function of varying the mismatch gain using the signals of recirculation pump runback, recirculation pump trip, feed water pump trip and reactor scram. CONSTITUTION:In a system controlling the liquid level in a boiling water reactor 1 at constant by using main steam flowrate signal 7, feed water flowrate signal 10 and reactor liquid level signal 2, the mismatch gain to convert the steam flowrate and the feed water flowrate signals to liquid level signal is increased by a mismatch gain setter 17 during the occurrence of events such as recirculation pump runback 24, recirculation pump trip 14, feed water pump trip 19 and reactor scram 16 and the feed water flow is reduced lower than in the actual time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor water supply control system for a boiling water nuclear power plant, and particularly, it attaches importance to stable operation of the reactor water level during normal operation and also when the transient event occurs. The present invention relates to a water supply control device that suppresses the rise of water quickly and performs optimum control.

[0002]

2. Description of the Related Art A conventional device, which changes the mismatch gain depending on the type of the feed pump or the number of operating pumps, is described in JP-A-56-96298.
The mismatch gain is changed by inserting the control rod described in Japanese Patent No. The above-mentioned invention switches the mismatch gain to an optimal value according to the type of the water supply pump or the number of operating pumps, and is intended to perform the optimum control in response to the state of the water supply system or the change of the state. is there. In the invention described below, the water level rises too much when the reactor water level is restored after the control rod is inserted with the main steam flow rate that decreases due to the insertion of the control rod and the supply water flow rate that increases so as to suppress the reactor water level that decreases with the insertion of the control rod. This is a method of increasing the mismatch gain and narrowing the water supply flow rate early so that there is no such problem.

[0003]

In the above prior art, the mismatch gain of the feed water control device is switched by controlling the state of the feed water system and the insertion of the control rod to control the reactor water level. In the event of a recirculation pump runback, a recirculation pump trip, or a reactor scrum event, the mismatch gain is not changed and the reactor water level rises, resulting in a high water turbine trip, etc. There was a possibility.

Further, in the above-mentioned prior art, the water level controllability at the time of trip of the water supply pump is not taken into consideration, and there is a tendency that the water level is greatly lowered.

The object of the present invention is to suppress the rise of the water level even when a transient event other than the insertion of the control rod occurs, and
An object of the present invention is to provide a reactor water supply control device for the purpose of preventing unnecessary plant shutdown and reactor isolation by suppressing the amount of water level drop at the time of trip of the water supply pump, improving the plant operation rate, and reducing the burden on operators. ..

[0006]

[Means for Solving the Problems] In order to achieve the above object, focusing on the mismatch gain of the feed water control system, the mismatch gain is increased when the water level rises or falls due to the mismatch between the main steam flow rate and the feed water flow rate. During normal operation other than that, the feedwater control system has a function to reduce the mismatch gain so that the response of the reactor water level is emphasized.

First, it will be briefly described whether or not the change in water level caused by the deviation (mismatch) between the main steam flow rate and the feed water flow rate can be suppressed by increasing the mismatch gain.

The water level of the reactor is the so-called amount of water in the reactor, and the amount of steam that exits the reactor (main steam flow rate).
It is closely related to the balance of the amount of water entering the reactor (supply flow rate). When the main steam flow rate is lower than the feed water flow rate, the reactor water level rises, and conversely, when the main steam flow rate is higher than the feed water flow rate, the reactor water level decreases.

This relationship is used with the mismatch gain,
It is a function that predicts and controls changes in the reactor water level in advance, by changing the deviation between the feed water flow rate and the main steam flow rate into a reactor water level signal. For this reason, when the mismatch gain is increased, the reactor water level change signal with respect to the deviation between the main steam flow rate and the feed water flow rate becomes large, and the control capability in advance is strengthened. As a result, the main steam flow rate and feed water flow rate change significantly, and as a result, when the water level changes due to deviation between the main steam flow rate and the feed water flow rate, the water level changes as the mismatch gain is larger because the control capability is stronger. Also becomes smaller. However, in a state where the main steam flow rate and the feed water flow rate do not change so much as in the normal operation state, when the operation is performed with a large mismatch gain, the response to the change in the reactor water level becomes slow. This is because when the feed water flow rate is changed with respect to the water level change, a mismatch occurs between the main steam flow rate and the feed water flow rate, and the control system works to suppress this change in the feed water flow rate. On the contrary, the response to the change in the water level becomes slower.

From the above, the mismatch gain is increased only when an abnormal transient change event occurs in the plant where the water level changes due to the mismatch between the main steam flow rate and the feed water flow rate. Therefore, the signals of abnormal transient change events are recirculation pump runback signal, recirculation pump trip signal,
The feedwater pump trip signal and the reactor scrum signal are imported to the reactor feedwater control device, and the mismatch gain is changed (increased).

[0011]

First, during the reactor scram, the reactor scrum crushes the voids in the core, lowering the reactor water level and increasing the feed water flow rate. On the other hand, the main steam flow rate decreases as the reactor power decreases due to scrum. For this reason, the reactor water level rises, but by increasing the mismatch gain, the advanced control capability is strengthened, and as shown in FIG. 3, the feedwater flow rate is narrowed down quickly and the reactor water level rise can be suppressed. ..

Next, at the time of the water supply pump trip, at this event, the water supply flow rate is reduced by the water supply pump trip and the reactor water level is lowered. However, even in this event, increasing the mismatch gain tends to increase the feedwater flow rate, so that the decrease in the reactor water level can be suppressed to a small level as shown in FIG.

Finally, during the recirculation pump trip and the recirculation pump runback, at this event, the main steam flow rate decreases due to the decrease in the reactor output, and the reactor water level rises due to the mismatch with the feed water flow rate. Also in this case, by increasing the mismatch gain, the advanced control capability is strengthened, and as shown in FIG. 5, the feedwater flow rate can be narrowed down quickly and the rise in the reactor water level can be suppressed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. This figure is a schematic diagram of an example of a boiling water nuclear power plant equipped with the reactor feedwater control device of the present invention. The water level control in the nuclear reactor 1 is performed by the following method. First, the reactor water level signal 2 was compared with the water level setting signal 4 set by the water level setting device 3, and the difference between the water level deviation signals 5 was calculated by multiplying the deviation between the main steam flow rate and the feed water flow rate by the mismatch gain. The water level deviation correction signal 2 which is a signal after adding the water level deviation prediction signal 20 is input to the water level controller 18. Then, the output signal of the water level controller (feed water flow rate request signal 22) is used to adjust the rotation speed of the water feed pump or the opening degree of the water feed adjustment valve, and the feed water flow rate is adjusted to keep the reactor water level constant. Further, the steam flow rate signal 7 is taken in from the main steam flow meter attached to the main steam pipe 6, and the feed water flow rate signal 10 is taken in from the feed water flow rate system meter attached to the water supply pipe 9.

Here, at the time of reactor scrum, feed water trip, recirculation pump trip and recirculation pump runback, reactor scrum signal 16, feedwater pump trip signal 19, recirculation pump trip signal 14, recirculation pump runback signal 24. Is taken into the mismatch gain setting device 17 from the safety protection system 15, the water supply pump 8, the recirculation pump 11 and the recirculation flow rate control device 13, and the mismatch gain is changed to suppress the fluctuation of the water level. The logic for changing the mismatch gain is shown in FIG. The mismatch gain setting device 17 is a mismatch amount signal 2 for the main steam flow rate and the feed water flow rate.
5 is a device for outputting the water level deviation prediction signal 20 by multiplying it by a mismatch gain. Here, the reactor scrum signal 16 from the safety protection system 15, the feed pump trip signal 19 from the feed pump 8, the recirculation pump trip signal 14 from the recirculation pump 11, the recirculation pump run from the recirculation flow controller 13 The back signal 24 is taken into the mismatch gain setting device 17, and these signals
Output signal from R circuit (mismatch gain change signal 2
According to 1), the water level deviation prediction signal 20 is switched from the output signal of the mismatch gain K1 to the output signal of the mismatch gain K2. This will change the mismatch gain during reactor scrum, feed pump trip, recirculation pump trip and runback.

The mismatch gain change signal can be reset after a predetermined time has elapsed, and is reset automatically or by a manual push button, and the mismatch gain is reset to a normal small value.

Next, how the water level fluctuation can be suppressed by changing the mismatch gain will be described below by taking the plant behavior at the time of scrum and the plant behavior at the time of trip of the feed pump as an example.

First, how the water level fluctuation (rise) is suppressed by the plant behavior during scrum and the movement of the control signal due to the mismatch gain change will be described with reference to FIG.

At the time of scram, first, the power is lowered by the full insertion of the control rods, and the voids in the core are crushed to reduce the water level. For this reason, the feedwater control system works to increase the feedwater flow rate and suppress the decrease in water level.However, because the main steam flow rate is decreasing due to the decrease in output, the reactor water level is reduced by the mismatch gain between the feedwater flow rate and the main steam flow rate. To rise. At this time, the feed water flow rate is narrowed down as the water level rises, but the narrowing start time and the narrowing amount differ depending on the mismatch gain. When the mismatch gain is increased, the water level deviation prediction signal with respect to the mismatch amount increases, so that the feedwater flow rate request signal is narrowed down quickly and large under the condition of main steam flowrate <feedwater flowrate. Therefore, as shown in the figure, when the mismatch gain is large, the control signal and the feed water flow rate are narrowed down quickly, and the rise in the water level can be suppressed to a small level.

Next, how the water level fluctuation (fall) is suppressed by the plant behavior of the feed water pump trip and the movement of the control signal due to the mismatch gain change will be described with reference to FIG. When the feed pump trips, the feed water flow is reduced and the reactor water level is lowered. For this reason, the water supply flow rate increases due to the function of the water supply control system, but the rate of increase at this time differs depending on the mismatch gain. When the mismatch gain is increased, the water level deviation signal with respect to the mismatch amount increases, so that the supply water flow rate request signal increases faster and increases under the condition of main steam flow rate> supply water flow rate. Therefore, as shown in FIG. 4, the larger the mismatch gain, the faster the control signal and the water supply flow rate increase, and the lowering of the water level can be suppressed.

Finally, during normal operation, the main steam flow rate and feed water flow rate do not fluctuate significantly in normal operation conditions. Therefore, if the mismatch gain is set to a large value, the response of the feed water flow rate when the reactor water level changes will be delayed. The reason for this will be described below. First, when the reactor water level fluctuates (rises), the feedwater control system acts to reduce the feedwater flow rate and try to suppress fluctuations in the reactor water level. Here, if the mismatch gain is large, a deviation occurs between the feed water flow rate and the main steam flow rate (feed water flow rate <main steam flow rate), and the water level deviation prediction signal increases to suppress the decrease in the feed water flow rate.

Therefore, the amount of rise in the reactor water level and the return of the reactor water level to the normal water level are delayed. This shows that the controllability is better when the mismatch gain is smaller during normal operation.

By adopting the water supply control device according to the present invention, the water level fluctuation at the time of an abnormal transient change such as a reactor scrum or a water supply pump trip can be suppressed, and the water level controllability during normal operation can be maintained.

[0024]

According to the present invention, in a boiling water nuclear power plant, the mismatch gain is changed by the reactor scrum signal, feed water pump trip signal, recirculation pump trip signal, and recirculation pump runback signal.
It is possible to minimize the occurrence of unnecessary alarms and trips, and to shorten the settling time of the reactor water level, thus reducing the burden on operators and improving the plant operating rate. ..

[Brief description of drawings]

FIG. 1 is a system diagram of a nuclear power plant having a mismatch gain changing function according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a mismatch gain setting device for changing the mismatch gain.

FIG. 3 is a comparative explanatory diagram of plant behavior when the mismatch gain is changed by the reactor scrum signal and when it is not.

FIG. 4 is a comparative explanatory diagram of plant behavior when the mismatch gain is changed by the feed pump trip signal and when it is not.

FIG. 5 is a comparative explanatory diagram of plant behavior when the mismatch gain is changed by the recirculation pump trip signal and the recirculation pump runback signal and when the mismatch gain is not changed.

[Explanation of symbols]

1 ... Reactor, 3 ... Water level setter, 6 ... Main steam flow rate, 8 ... Water supply pump, 9 ... Water supply flow rate, 11 ... Recirculation pump, 12 ...
Recirculation flow rate, 13 ... Recirculation flow rate control device, 15 ... Safety protection system, 17 ... Mismatch gain setting device, 18 ... Water level controller.

Claims (1)

[Claims] 1. In a boiling water nuclear power plant, when an abnormal state of a plant such as a recirculation pump runback, a recirculation pump trip, a feedwater pump trip, and a reactor scram occurs, the amount of mismatch between the main steam flow rate and the feedwater flow rate is adjusted to A reactor water supply control device characterized by changing a mismatch gain, which is a correction constant converted into a reactor water level.